This disclosure relates to block copolymers and to brushes that are disposed upon a substrate and that can be used to control block copolymer characteristics. Controlling block copolymer characteristics can be used to manufacture semiconductors that have dimensions in the nanometer range.
Modern electronic devices are moving toward utilization of structures that have a periodicity of less than 40 nanometers. The ability to shrink the size and spacing of various features on a given substrate (e.g., gates in field effect transistors) is currently limited by the wavelength of light used to expose photoresists (i.e., 193 nm). These limitations create a significant challenge for the fabrication of features having a critical dimension (CD) of <50 nm.
Block copolymers have been proposed as one solution to formation of patterns with periodicity of less than 40 nanometers. Block copolymers form self-assembled nanostructures in order to reduce the free energy of the system. Nanostructures are those having average largest widths or thicknesses of less than 100 nanometers. This self-assembly produces periodic structures as a result of the reduction in free energy. The periodic structures can be in the form of domains, lamellae or cylinders. Because of these structures, thin films of block copolymers provide spatial chemical contrast at the nanometer-scale and, therefore, they have been used as an alternative low-cost nano-patterning material for generating periodic nanoscale structures.
Many attempts have been made to develop copolymers and processes for patterning. FIGS. 1A and 1B depict examples of lamellar forming block copolymers that are disposed upon a substrate. The block copolymer comprises a block A and a block B that are reactively bonded to each other and that are immiscible with each other. The alignment of the lamellar domains can be either parallel (FIG. 1A) or perpendicular (FIG. 1B) to the surface of a substrate surface upon which they are disposed. The perpendicularly oriented lamellae provide nanoscale line patterns, while there is no surface pattern created by parallel oriented lamellae.
Where lamellae form parallel to the plane of the substrate, one lamellar phase forms a first layer at the surface of the substrate (in the x-y plane of the substrate), and another lamellar phase forms an overlying parallel layer on the first layer, so that no lateral patterns of microdomains and no lateral chemical contrast form when viewing the film along the perpendicular (z) axis. When lamellae form perpendicular to the surface, the perpendicularly oriented lamellae provide nanoscale line patterns.
Cylinder forming block copolymers, on the other hand, provide nanoscale line patterns when the cylinders form parallel to the surface and hole or post patterns when the cylinders form perpendicular to the surface. Therefore, to form a useful pattern, control of the orientation of the self-assembled microdomains in the block copolymer is desirable. A schematic of the process using a sphere or cylinder forming block copolymer is shown in FIGS. 1(C) and 1(D). The block copolymer is applied to a substrate such as a trench treated with a brush layer. After annealing to form and align the domains, one block is selectively removed with an etch or development process to provide a mask that can be transferred into the substrate to create a nanoscale pattern with smaller features than in the original trench substrate.
The block copolymer is desirably annealed with heat (in the presence of an optional solvent), which allows for microphase separation of the polymer blocks A and B at a temperature above the glass transition temperature and below the order to disorder transition temperature. The annealed film can then be further developed by a suitable method such as immersion in a solvent/developer or by reactive ion etching which preferentially removes one polymer block and not the other to reveal a pattern that is commensurate with the positioning of one of the blocks in the copolymer.
The use of conventional block copolymers present difficulties in orientation control and long range ordering during the self assembly process. Diblock copolymers of poly(styrene) and poly(dimethylsiloxane) (PS-b-PDMS) offer promise for application in the patterning of nanoscale dimensions (especially sub-45 nm) using directed self assembly techniques. The etch selectivity between the polystyrene and poly(dimethylsiloxane) domains makes these materials useful for patterning. These materials are generally employed in so-called graphoepitaxy directed self-assembly (DSA) processes where physical confinement such as a hole or trench is used to align the block copolymer morphology. In Nano Lett. 2007, 7, 2046, Jung and Ross described the use of PS-b-PDMS in long trenches, resulting in aligned PDMS cylinders. After alignment in trenches and etching, the siloxane material forms a resist line pattern within the SiO2 lines to multiply the feature density. Trench-patterned Si substrates with native oxide layers were first coated with a hydroxyl-end functional PDMS brush polymer (PDMS-OH) before application and annealing of the PS-b-PDMS. However, PDMS-OH is undesirable for a brush material due to the oxygen etch resistance of the PDMS, as the PDMS layer at the bottom of the trenches would make pattern transfer difficult. Alternatively, hydroxyl-end functional polystyrene brush polymers (PS-OH) have been used to treat trench substrates before application and annealing of the PS-b-PDMS.
Conventional wisdom in the art, however, is that the use of PS-b-PDMS block copolymers in such operations cannot effectively be thermally annealed due to the large incompatibility between the polystyrene and polydimethylsiloxane blocks. This is especially apparent in PS-b-PDMS materials that display a spacing of 30 nm or larger. For any block copolymer system, as the interdomain spacing increases, the material becomes more difficult to anneal to low defectivity. Accordingly, those in the art have developed a variety of alternative techniques for processing of block copolymers like poly(styrene)-b-poly(dimethylsiloxane) block copolymers. For example, Jung and Ross employed solvent vapor annealing to align the PS-b-PDMS, and in U.S. Patent Publication No. 2011/0272381; Millward, et al., disclose a solvent annealing method for processing diblock copolymer films such as poly(styrene)-b-poly(dimethylsiloxane).
In some DSA schemes, it is also desirable for the lines and spaces to have matching critical dimensions (CD). For example, it is possible to have at least two distinct populations of space CD after etch, one formed between the SiO2 guide and the adjacent siloxane cylinder (the guide-adjacent space) and another between siloxane cylinders (the inter-cylinder space). It can be difficult to achieve matching space CDs as the guide-adjacent space CD is often smaller than the inter-cylinder space CD space CDs, particularly with block copolymers of large pitch (L0>30 nm).
Notwithstanding, there remains a need for new combinations of block copolymer and brush compositions for use in patterning substrates. In particular, there remains a need for new copolymer compositions that enable patterning on intermediate length scales of 20 to 40 nm and that preferably exhibit a fast annealing profile with low defect formation. There is also a need to enable large guide adjacent space critical dimensions in trench guided directed self assembly applications.
It is therefore desirable to find combinations of block copolymers and brushes that can generate self-assembled films having domain sizes of less than 25 nanometers with a periodicity of less than 50 nanometers. Additionally, it is desirable to find combinations of block copolymers and brushes where the block copolymers contain a minority block with high etch resistance and a matrix block with comparatively low etch resistance, and the brushes have varying surface energy and coating thickness properties and low etch resistance compared to the etch resistant block. Additionally, it is desirable to find combinations of block copolymers and brushes where the block copolymers contain polymers with low silicon content and etch resistant silicon-containing polymers and the brushes contain polymers with low silicon content that are different from the organic polymer in the block copolymer.